1. Field of the Invention
The present invention relates to a normal force applicator and removal apparatus for applying and removing a normal force to a document stack and a shingler wheel movable to accommodate multiple document stack lengths, and more specifically, to accomplish the foregoing while decreasing the normal force as the document stack is depleted to shingle documents at a substantially predetermined constant rate.
2. Prior Art
The technological advances made in the speed of producing a copy sheet from a document, in an electrophotographic copier system, has necessitated the development of automatic document feeders (ADF) and recirculating automatic document feders (RADF) to enable the aforementioned electrophotographic copier system to produce copy sheets at its full speed rate. Accordingly, the prior art is replete with such automatic feeder devices.
Some of the techniques in document feeders, used to separate documents from a document stack include belt separators, vacuum separators, friction roller separators and combing wheel, wave generator or shingler wheel type separators.
Each of the foregoing types of document feeders have advantages and disadvantages and require, in varying degrees, unique and highly specialized cooperating devices to properly separate documents from a document stack for subsequent processing. In the present invention, a modern version of the combing wheel is used to feed or shingle documents from a document stack to generate a shingled stack. Unique problems are presented when a combing wheel is used to feed documents from the bottom of a document stack as opposed to the more common use of a combing wheel to feed documents from the top of a document stack as will be described. The present invention is concerned with a normal force applicator and removal apparatus for cooperating with a combing wheel feeding or shingling sheets from the bottom of a stack.
A modern version of a combing wheel suitable to be used with the present invention is disclosed in U.S. Pat. No. 4,126,305 to Colglazier, et al, entitled "Combing Wheel," filed Apr. 18, 1977, patented Nov. 21, 1978 and assigned to the same assignee as the present invention. Also, the use of combing wheel type feeders to feed cut sheets to a printer is documented in several U.S. Patents to Dummer. Exemplary examples are: U.S. Pat. No. 566,670 to Dummer entitled "Paper Feeding Machine," issued on Aug. 25, 1896 from application Ser. No. 491,760, filed Nov. 28, 1893; and U.S. Pat. 781,504 to Dummer entitled "Paper Feeding Machine," issued on Jan. 31, 1905 from Application Ser. No. 734,030, filed Oct. 18, 1899.
Modern applications of the combing wheel technology are disclosed in serveral IBM Technical Disclosure Bulletin Articles. Exemplary examples are: Hunt, "Envelope Shingling Apparatus," Vol. 19, No. 10, March 1977, pgs. 3628-3629; Hunt, "Cover Sheet Feeding Apparatus," Vol. 19, No. 10, March 1977, pg. 3630; Hunt et al, "Sheet Shingler," Vol. 20, No. 2, July 1977, pg. 497; Avritt, "Bottom Sheet Paper Feed," Vol. 20, No. 2, July 1977, pg. 496; Hunt, "Trailing Edge Paper Feeding Apparatus," Vol. 20, No. 5, October 1977, pg. 1678; Fallon et al, "Sheet Shingler," Vol. 21, No. 2, July 1978, pgs. 477-478; Rosati, "Jam-Free Shingling Aperture," Vol. 21, No. 9, February 1979, pg. 3530; Markham et al, "Shingling Depletion Sensor," Vol. 21, No. 9, February 1979, pgs. 3538-3539; Markham et al, "Double Restraint Gate for Wave-Generator Feeder System" Vol. 21, No. 9, February 1979, pgs. 3540-3542; and Fallon et al, "Sheet Feed Apparatus," Vol. 21, No. 12, May 1979, pgs. 4765-4767.
The present invention incorporates a unique normal force applicator and removal apparatus in cooperation with a combing wheel, wave generator or shingler wheel type feeder disposed to feed from the bottom of a document stack. The normal force applicator and removal apparatus is configured and operated such that most of the problems associated with this bottom type feeder system are eliminated. The problems solved by the present invention and the consequences of their solution are that the shingled stack is not skewed; the rate of shingling is controllable and predictable regardless of the kind or condition of the documents in the document stack and regardless of the height of the document stack; and, the risk of damage to light-weight documents, especially if the document stack is near depletion, is minimized.
As aforementioned, in document feeders and sheet feeders, various techniques have been used to separate sheets or documents from a stack. One example is U.S. Pat. No. 3,861,671 to Hoyer, entitled "Liftable Bail Bar for Allowing Return of Multi-Ply Separated Sheets to Stack" which discloses a bail bar for forcing a stack of sheets against a separator roller (friction type) thereunder to provide a normal force to assist in the feeding of sheets singularly from the stack. Provided downstream of the separator roller is a feed roller for feeding a single sheet forward and a reversing roller for returning any erroneously fed multiple sheets, other than the single sheet, back to the stack. The bail bar is liftable from atop the stack to minimize drag on a separated sheet and to allow the multiple fed sheet pushed towards the stack by the reversing roller to be returned thereto.
Another example is U.K. Pat. No. 1,427,357 to Brooke, entitled "Sheet Feeding Method," which discloses a system for feeding copy sheets from a stack to a transfer station, in an electrophotographic copier, such that a wave is created in at least the uppermost sheet(s) in the stack when it is contacted intermittently by freely rotatable rollers in cooperation with radially extending arms.
Yet another example is U.S. Pat. No. 3,008,709 to Buslik, entitled "Sheet Separating and Feeding Apparatus," which discloses a sheet separating and feeding apparatus for successively separating the top sheets of a stack of sheets, and for feeding the successively separated sheets from the stack. The apparatus is capable of handling a stack of mixed sheets in which the sheets may be of various materials of nonuniform dimensions and weight. The separator member (a shingler wheel) is mounted by a shaft for movement between an active position and an inactive position and is disposed adjacent to the stack of documents so that rotatable members, included therein, are rotatable in a plane substantially parallel with the sheets in the stack. Hence, when contact of the separator member is made with the uppermost sheets of the stack, they are simultaneously displaced in varying degrees about the axis of rotation of the shaft of the separator member in a fan-like fashion.
Still another example is U.S. Pat. No. 781,504 to Dummer, entitled "Paper-Feeding Machine," which discloses an apparatus comprising a separating mechanism, i.e., a shingler wheel, by which sheets are fanned out from a stack thereof located on a convex support surface of the separating mechanism formed by a number of traverse rollers which are caused to rotate opposite and in conformity to the convex surface. In addition, a device for regulating the movement of the rollers to engage the delivery of the sheets individually as required by an associated machine to be fed is also disclosed. In this reference, mention is made of U.S. Pat. Nos. 566,670 and 566,671 also to Dummer and relating to the same subject matter. As far as is known, these two references are the earliest patented use for a combing wheel, wave generator or shingler type feeder.
While the foregoing references disclose combing wheel, wave generator or shingler wheel type of feeders, (see, for example, Brooke, Buslik or Dummer), and a bail bar, i.e., a normal force applicator, cooperating with a separator means, i.e., a friction roller (see, for example, Hoyer), the prior art is not concerned with the previously mentioned problems solved by the present invention. Consequently, there is no teaching separately or in combination of the use of a normal force applicator and removal apparatus in combination with a bottom disposed shingler wheel for shingling at a substantially constant predetermined rate to maintain a shingled stack of documents regardless of the height of the document stack while substantially eliminating skewing of the shingled stack. Hence, there is a need in the prior art for a device such as disclosed and claimed herein.
The prior art, as indicated hereinabove, includes some advances in combing wheels, wave generator or shingler wheel type feeders, and some advances in bail bar or normal force applicators. However, insofar as can be determined, no prior art device or method incorporates the features and advantages of the present invention.